Semiconductor manufacturing has historically used wet chemical stripping tools to remove flux from wafer surfaces for many years. This process had typically employed heated solvents (such as 1,3,5 trimethylbenzene) to strip the flux. These solvents served to execute the process but were not environmentally friendly. Advancements in flux technology created capable fluxes that could be stripped with more environmentally friendly chemistry (such as long chain alcohols). Continued refinement in flux technology has now yielded water soluble flux.
The process involved to remove water soluble flux for one wafer typically involves a ten minute DI (deionized water) flow rate of 2 LPM with a temperature of over 80° C. This water is used in a single pass. Semiconductor tools for volume manufacturing are built to process multiple wafers simultaneously. Accordingly, the large volume of hot DI employed to strip the flux yields the same large volume of heated DI going down the drain. Semiconductor fab facilities are typically not designed to handle these large volumes of heated fluids. Fab facilities sought to halt operations of the flux removal tool until the fluid discharge temperature could be brought down to an acceptable temperature.
Initial attempts were made to reduce the discharge fluid temperature to drain via dilution. The 2 LPM of 65° C. DI required 6 LPM of 25° C. DI to bring the temperature of the mixture to 35° C. This raised water usage volume (e.g., an increase of 3×) and was unacceptable. The use of a heat exchanger to have incoming water cool down the heated discharge stream was not possible. There was insufficient room within the tool to mount a large heat exchanger internally, also there was no unoccupied space in the immediate vicinity of the tool as it was installed inside the semiconductor lab. The energy being supplied for four chambers operating in parallel is some 30 kW. Mechanical refrigeration would require a large unit and be costly to install and operate with all of issues of the water heater exchanged previously noted.
In accordance with the present invention, the fluid discharge temperature was lowered into the acceptable range through the use of refrigerative exhaust. The 80° C. processing water dropped to 65° C. during the flux removal process. The 65° C. discharge fluid was introduced to the top of the existing main cabinet exhaust duct through one or more nozzles. The hot fluid discharge flowed down the exhaust duct, while ambient exhaust was pulled up through the duct at normal (310 SCFM) exhaust rates. Engineered internals placed within the duct enhanced the fluid/exhaust interface. Thus 30° C. cooling was obtained through sensible and latent heat loss from the discharge fluid and sensible heat gain from the exhaust (make up air warming as it was drawn through the exhaust duct) combined with mass transfer in the form of a small amount of water vapor being introduced into the exhaust stream. The largest piece of hardware required for this cooling operation is the exhaust duct, which was an existing piece of hardware within the tool. Accordingly, fitting in the support hardware was possible in the small amount of unoccupied space within the tool and no space external to the tool was required.